The present invention relates to the grinding method with simultaneous homogenization of powder materials with liquid components and can be used in industries producing composites based on disperse powder materials, such as talc, kaolin, gypsum bound by thermoplastic or other liquid plastic binders as well as in chemical and other industries.
The peculiar characteristics of roller breakers also capable to homogenize composite materials are their relatively small sizes, low noise level, optimal distribution of mechanical power for material processing at effective power consumption compared to drum, bead and hammer mills. Roller breakers are quite flexible to be readjusted to obtain the required degrees of grinding and homogenization.
The most effective ways for grinding fine dispersed materials are attrition grinding and crushing.
There are known cone-shaped rolling mills used for pulverized coal fuels manufactured by OJSC “Tyazhmash”. These mills work by breaking original solid particles using cone-shaped rolls interacting with flat or sloped parts. The material passes through the bites and breaks as a result of being crushed.
These machines ensure effective grinding but due to their design they do not allow to provide homogenization of the mill material with a liquid component, e.g., using hot melts of such thermoplastic polymers as polyethylene, polypropylene etc. This ay be due to the design features of these mills or different rotation velocities of rotating crashing rolls and barrels and flat or sloped counterparts of the mechanisms that ensure only breaking of the material and do not allow the material being homogenized to circulate between crushing rolls during processing of the material.
There is a known roller breaker (Patent RU N 2132233, MPK B02C 4/24 published on 27 Jun. 1999) which includes cone-shaped backing and driven rolls mounted on the frame with their large bases facing opposite directions, and a driving mechanism. The shaft of the driven roll has two pulleys with cam gears installed in bearings on its ends. The latter have a drive which is connected with the two pulleys via a belt drive, and the driven roller itself is spring-loaded.
In this case the weight of cam gears and total weight of pulleys with driven shaft cam gears and bearings are defined by the dependencies making a connection between the weight of cam gears, pulley rotation velocity, eccentricity, spring tension, spring prestrain and total weight of pulleys with driven shaft cam gears and bearings.
According to this patent the device can be operated only in pre-resonant mode restricted by the above stated dependencies, and in this case the breaking effect is achieved due to impact-vibration action on the material in the bite between backing and driven rolls resulting in the restricted capacity control due to the fact that both rolls are working in the pre-resonant mode.
One of the disadvantages is that grinding in this device is performed when the rolls are being rotated with maximum effect at the moment corresponding to such a position of cam gears when their oscillation impact vector coincides with the direction of interaxial horizontal of the rolls and is directed to the backing roll, i.e. only once during a complete rotation of the rolls leading to the reduction of grinding capacity.
In case a bite between the rolls is maximally opened, at the moment when the oscillation impact vector of the cam gears is directed horizontally opposite to the backing roll, the mill material undergoes minimal force action.
All the above factors result in that the mill material will have a variable degree of dispersion when passing through a bite between the rolls during each rotation cycle of the latter with the most effective impact on the material achieved within not more that a quarter of the time required for one rotation of the driven roll. Besides, the two pulleys with a flexible drive are not capable of ensuring stable rotation velocity of the driven roller due to unavoidable frictional sliding of such drives in oscillation rotation mode of the pulleys having cam gears.
The closest to the present invention is a roller mill (USSR Inventor's Certificate N 354886, MPK B02C 4/30 published on 16 Oct. 1972 and dependent on Inventor's Certificate N 287511, MPK B02C4/04 published on 15 Nov. 1970).
According to Inventor's Certificate N 354886 the two rolls of this mill are cone-shaped, and a profiled surface of both rotating rolls is made in the form of longitudinal grooves and, besides, one of the rolls has grooves with V-shaped extending profile and the other has deep egg-shaped grooves. According to this invention the roller mill is designed to be used for grinding and homogenization of different organic pigments and semiproducts containing crystalline materials. The disadvantage of this device is that it can be operated only provided a mixture of basic liquid and powder components is made pasty before the process starts. This implies the use of some additional device, e.g., a mixer. Another disadvantage of this invention is that the longitudinal grooves, and the deep egg-shaped grooves in particular, act as stagnation areas where the paste being processed and its powder component in the first place is almost not subject to grinding, therefore reducing the grinding quality of the powder component and the production efficiency of the mill. The main purpose of this mill is dispersing and, to be more exact—homogenization of the prepared paste, and, in spite of the claimed cone shape of the rolls with the reverse arrangement of their similar end surfaces, the grinding effect for the powder component of the material being processed typical for cone-shaped roller mills is practically not achieved.
It should also be stated that different profiled surfaces of the grooves on the rolls make the process of their manufacturing quite complicated.